Make your espresso strong, as you would for drinking, and pour it into a wide, shallow dish so it cools quickly and gives the ladyfingers plenty of room later. Stir in the Marsala or rum if you're using it, then set the dish aside and let it come fully to room temperature. This is not a step to rush — warm coffee will turn your savoiardi to porridge the moment they touch it, and a good tiramisù depends on patience long before it depends on skill.

In a heatproof bowl set over a pot of gently simmering water, not touching the water itself, whisk the egg yolks with the sugar and the pinch of salt constantly and without stopping. You are making what we call a zabaione, and you want it to turn pale, thick, and ribbon-like, reaching about 71°C or 160°F on a thermometer if you have one, which takes roughly five to eight minutes. This gentle cooking is what makes the eggs safe to eat without scrambling them, so keep the heat low and your wrist moving the whole time. If you already have pasteurized eggs from a carton, you may skip the stovetop, but I always cook mine this way — it gives the cream a rounder, almost custardy flavour.

Lift the bowl off the heat and whisk the yolk mixture for another minute or two off the stove so it stops cooking and cools slightly. Add the mascarpone in two additions, folding gently with a spatula rather than beating it, lifting from the bottom of the bowl up and over. Because your mascarpone is at room temperature, it will fold in smoothly without lumps — cold mascarpone straight from the fridge will fight you every time, so don't skip that detail.

In a separate clean bowl, whip the cold heavy cream until it holds soft peaks, no further, since overwhipped cream turns grainy once folded into the mascarpone. Fold the whipped cream into the mascarpone mixture in two additions, working gently so you don't knock the air back out. This is the secret to a tiramisù that feels like a cloud on the fork rather than a dense cheesecake — the air you fold in now is what you'll taste later.

Working one at a time, dip each savoiardo into the cooled coffee for no more than one second on each side — you want it glistening and damp, never dripping or soft in your fingers. Arrange the dipped ladyfingers snugly in a single layer at the bottom of your serving dish, breaking pieces as needed to fill the corners. Remember that the biscuit keeps drinking in moisture as it sits in the fridge overnight, so a quick dip now is what keeps the finished dessert sliceable instead of soupy.

Spread half of the mascarpone cream evenly over the first layer of ladyfingers, smoothing it with the back of a spoon or an offset spatula right to the edges of the dish. Add a second layer of coffee-dipped savoiardi on top, then finish with the remaining mascarpone cream, smoothing the surface as flat and even as you can manage. A flat top isn't just for looks — it means the cocoa you dust on later will sit evenly across every slice.

Cover the dish and refrigerate for at least six hours, though overnight is truly best, so the layers have time to settle into one another and the flavours deepen. Just before serving, dust the top generously with cocoa powder through a fine sieve — wait until this moment rather than doing it earlier, or the cocoa will absorb moisture and turn dull and clumpy instead of staying dark and powdery. Cut clean slices with a knife warmed under hot water and wiped dry between cuts, and serve it cold, straight from the fridge.